The present invention is directed to improved photosensitive imaging members. More specifically, the present invention is directed to photosensitive imaging members containing improved charge transport layers. One embodiment of the present invention is directed to an imaging member which comprises a conductive substrate, a photogenerating material, and a polymer of the formula ##STR1## wherein x is an integer of 0 or 1, A is ##STR2## or mixtures thereof, B is ##STR3## wherein v is an integer of from 1 to about 20, EQU --(CH.sub.2 O).sub.t --
wherein t is an integer of from 1 to about 20, ##STR4## wherein z is an integer of from 2 to about 20, ##STR5## wherein u is an integer of from 1 to about 20, ##STR6## wherein w is an integer of from 1 to about 20, ##STR7## wherein (1) Z is ##STR8## wherein p is 0 or 1; (2) Ar is ##STR9## (3) G is an alkyl group selected from alkyl or isoalkyl groups containing from about 2 to about 10 carbon atoms; (4) Ar' is ##STR10## (5) X is ##STR11## wherein s is 0, 1, or 2, ##STR12## and (6) q is 0 or 1; or mixtures thereof, wherein at least some of the "B" groups are of the formula ##STR13## C is ##STR14## or mixtures thereof, wherein R is an alkyl group, an aryl group, an arylalkyl group, or mixtures thereof, and m and n are integers representing the number of repeating units.
The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. The basic electrophotographic imaging process, as taught by C. F. Carlson in U.S. Pat. No. 2,297,691, entails placing a uniform electrostatic charge on a photoconductive imaging member, exposing the imaging member to a light and shadow image to dissipate the charge on the areas of the imaging member exposed to the light, and developing the resulting electrostatic latent image by depositing on the image a finely divided electroscopic material known as toner. In the Charge Area Development (CAD) scheme, the toner will normally be attracted to those areas of the imaging member which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This developed image may then be transferred to a substrate such as paper. The transferred image may subsequently be permanently affixed to the substrate by heat, pressure, a combination of heat and pressure, or other suitable fixing means such as solvent or overcoating treatment.
Imaging members for electrophotographic imaging systems comprising selenium alloys vacuum deposited on substrates are known. Imaging members have also been prepared by coating substrates with photoconductive particles dispersed in an organic film forming binder. Coating of rigid drum substrates has been effected by various techniques such as spraying, dip coating, vacuum evaporation, and the like. Flexible imaging members can also be manufactured by processes that entail coating a flexible substrate with the desired photoconducting material.
Some photoresponsive imaging members consist of a homogeneous layer of a single material such as vitreous selenium, and others comprise composite layered devices containing a dispersion of a photoconductive composition. An example of a composite xerographic photoconductive member is described in U.S. Pat. No. 3,121,006, which discloses finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. Imaging members prepared according to the teachings of this patent contain a binder layer with particles of zinc oxide uniformly dispersed therein coated on a paper backing. The binders disclosed in this patent include materials such as polycarbonate resins, polyester resins, polyamide resins, and the like.
Photoreceptor materials comprising inorganic or organic materials wherein the charge generating and charge transport functions are performed by discrete contiguous layers are also known. Additionally, layered photoreceptor members are disclosed in the prior art, including photoreceptors having an overcoat layer of an electrically insulating polymeric material. Other layered photoresponsive devices have been disclosed, including those comprising separate photogenerating layers and charge transport layers as described in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. Photoresponsive materials containing a hole injecting layer overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer, and a top coating of an insulating organic resin, are disclosed in U.S. Pat. No. 4,251,612, the disclosure of which is totally incorporated herein by reference. Examples of photogenerating layers disclosed in these patents include trigonal selenium and phthalocyanines, while examples of transport layers include certain aryl diamines as illustrated therein.
In addition, U.S. Pat. No. 3,041,167 discloses an overcoated imaging member containing a conductive substrate, a photoconductive layer, and an overcoating layer of an electrically insulating polymeric material. This member can be employed in electrophotographic imaging processes by initially charging the member with an electrostatic charge of a first polarity, followed by exposing it to form an electrostatic latent image that can subsequently be developed to form a visible image.
Japanese Patent Publication 63-247757 A2, the disclosure of which is totally incorporated herein by reference, discloses an electrophotographic photosensitive body consisting of a body in which a photoconductive layer laminated on a conductive support contains a charge generating substance and/or a charge transporting substance, and at least one polyether ketone polymer consisting of structural units which can be expressed by the following general formulae (I) and (II) ##STR15## wherein m is 0 or 1 and Ar indicates ##STR16## wherein R is an alkyl group, n is 0, 1, or 2, and X indicates ##STR17## with R' and R" each independently indicating --H, --CH.sub.3, --C.sub.2 H.sub.5, ##STR18## wherein the proportion of structural units in the polymer expressed by the general formula (I) is from 0.1 to 1.0 and the proportion of structural units in the polymer expressed by the general formula (II) is 0 to 0.9.
U.S. Pat. No. 5,336,577 (Spiewak et al.), the disclosure of which is totally incorporated herein by reference, discloses a thick organic ambipolar layer on a photoresponsive device which is simultaneously capable of charge generation and charge transport. In particular, the organic photoresponsive layer contains an electron transport material such as a fluorenylidene malonitrile derivative and a hole transport material such as a dihydroxy tetraphenyl benzadine containing polymer. These may be complexed to provide photoresponsivity, and/or a photoresponsive pigment or dye may also be included.
U.S. Pat. No. 4,801,517 (Frechet et al.), the disclosure of which is totally incorporated herein by reference, discloses an electrostatographic imaging member and an electrophotographic imaging process for using the imaging member in which the imaging member comprises a substrate and at least one electroconductive layer, the imaging member comprising a polymeric arylamine compound represented by the formula ##STR19## wherein n is between about 5 and 5,000, m is 0 or 1, Z is selected from certain specified aromatic and fused ring groups, Ar is selected from certain specified aromatic groups, R is selected from certain specified alkyl groups, Ar' is selected from certain specified aromatic groups, and R' and R" are independently selected from certain specified alkylene groups.
U.S. Pat. No. 4,806,443 (Yanus et al.), the disclosure of which is totally incorporated herein by reference, discloses an electrostatographic imaging member and an electrophotographic imaging process for using the imaging member in which the imaging member comprises a substrate and an electroconductive layer, the imaging member comprising a polymeric acrylamine compound represented by the formula ##STR20## wherein n is between 5 and about 5,000, m is 0 or 1, y is 1, 2, or 3, Z is selected from certain specified aromatic and fused ring groups, Ar is selected from certain specified aromatic groups, Ar' is selected from certain specified aromatic groups, and X' is an alkylene radical selected from the group consisting of alkylene and isoalkylene groups containing 2 to 10 carbon atoms. The imaging member may comprise a substrate, charge generation layer, and a charge transport layer.
U.S. Pat. No. 4,806,444 (Yanus et al.) and U.S. Pat. No. 4,935,487 (Yanus et al.), the disclosures of each of which are totally incorporated herein by reference, disclose an electrostatographic imaging member and an electrophotographic imaging process for using the imaging member in which the imaging member comprises a substrate and an electroconductive layer, the imaging member comprising a polymeric arylamine compound represented by the formula ##STR21## wherein n is between about 5 and about 5,000, m is 0 or 1, Z is selected from certain specified aromatic and fused ring groups, Ar is selected from certain specified aromatic groups, and Ar' is selected from certain specified aromatic groups. The imaging member may comprise a substrate, charge generation layer, and a charge transport layer.
U.S. Pat. No. 4,818,650 (Limburg et al.) and U.S. Pat. No. 4,956,440 (Limburg et al.), the disclosures of each of which are totally incorporated herein by reference, disclose an electrostatographic imaging member and an electrophotographic imaging process for using the imaging member in which the imaging member comprises a substrate and at least one electroconductive layer, the imaging member comprising a polymeric arylamine compound represented by the formula ##STR22## wherein R is selected from the group consisting of --H, --CH.sub.3, and --C.sub.2 H.sub.5, m is between about 4 and about 1,000, A is selected from the group consisting of an arylamine group represented by the formula ##STR23## wherein m is 0 or 1, Z is selected from certain specified aromatic and fused ring groups that also contain an oxygen or sulfur atom, certain linear or cyclic hydrocarbon groups, and certain amine groups, Ar is selected from certain specified aromatic groups, Ar' is selected from certain specified aromatic groups, and B is selected from the group consisting of the arylamine group as defined for A and EQU --Ar--V).sub.n AR--
wherein Ar is as defined above and V is selected from an oxygen or sulfur atom, certain linear or cyclic hydrocarbon groups, or a phenylene group, and at least A or B contains the arylamine group. The imaging member may comprise a substrate, charge generation layer, and a charge transport layer.
U.S. Pat. No. 5,030,532 (Limburg et al.), the disclosure of which is totally incorporated herein by reference, discloses an electrostatographic imaging member comprising a support layer and at least one electrophotoconductive layer, said imaging member comprising a polyarylamine polymer represented by the formula ##STR24## wherein n is between about 5 and about 5,000, or 0 if p&gt;0, o is between about 9 and about 5,000, or is 0 if p&gt;0 or n=0, p is between about 2 and about 100, or is 0 if n&gt;0, X' and X" are independently selected from a group having bifunctional linkages, Q is a divalent group derived from certain hydroxy terminated arylamine reactants, Q' is a divalent group derived from a hydroxy terminated polyarylamine containing the group defined for Q and having a weight average molecular weight between about 1,000 and about 80,000, and the weight average molecular weight of the polyarylamine polymer is between about 10,000 and about 1,000,000.
Copending application U.S. Ser. No. (not yet assigned; Attorney Docket No. D/96194, filed concurrently herewith, with the named inventors Timothy J. Fuller, Leon A. Teuscher, John F. Yanus, Damodar M. Pai, Kathleen M. Carmichael, Edward F. Grabowski, and Paul F. Zukoski, the disclosure of which is totally incorporated herein by reference, discloses an imaging member which comprises a conductive substrate, a photogenerating material, and a binder comprising a polymer selected from (a) those of the formulae ##STR25## wherein x is an integer of 0 or 1, A is ##STR26## or mixtures thereof, B is ##STR27## wherein v is an integer of from 1 to about 20, EQU --(CH.sub.2 O).sub.t --
wherein t is an integer of from 1 to about 20, ##STR28## wherein z is an integer of from 2 to about 20, ##STR29## wherein u is an integer of from 1 to about 20, ##STR30## wherein w is an integer of from 1 to about 20, ##STR31## or mixtures thereof, C is ##STR32## or mixtures thereof, wherein R is an alkyl group, an aryl group, an arylalkyl group, or mixtures thereof, and m and n are integers representing the number of repeating units; (b) those of the formulae ##STR33## wherein x is an integer of 0 or 1, A is ##STR34## or mixtures thereof, B is ##STR35## wherein v is an integer of from 1 to about 20, EQU --(CH.sub.2 O).sub.t --
wherein t is an integer of from 1 to about 20, ##STR36## wherein z is an integer of from 2 to about 20, ##STR37## wherein u is an integer of from 1 to about 20, ##STR38## wherein w is an integer of from 1 to about 20, ##STR39## or mixtures thereof, C is ##STR40## or mixtures thereof, wherein R is an alkyl group, an aryl group, an arylalkyl group, or mixtures thereof, and m and n are integers representing the number of repeating units; (c) those of formulae I, III, IV, VII, or VIII wherein x is an integer of 0 or 1, A is ##STR41## B is ##STR42## wherein v is an integer of from 1 to about 20, EQU --(CH.sub.2 O).sub.t --
wherein t is an integer of from 1 to about 20, ##STR43## wherein z is an integer of from 2 to about 20, ##STR44## wherein u is an integer of from 1 to about 20, ##STR45## wherein w is an integer of from 1 to about 20, ##STR46## or mixtures thereof, C is ##STR47## or mixtures thereof, wherein R is an alkyl group, an aryl group, an arylalkyl group, or mixtures thereof, and m and n are integers representing the number of repeating units; (d) those of formulae I, III, IV, VII, and VIII wherein x is an integer of 0 or 1, A is ##STR48## B is ##STR49## wherein v is an integer of from 1 to about 20, EQU --(CH.sub.2 O).sub.t --
wherein t is an integer of from 1 to about 20, ##STR50## wherein z is an integer of from 2 to about 20, ##STR51## wherein u is an integer of from 1 to about 20, ##STR52## wherein w is an integer of from 1 to about 20, ##STR53## or mixtures thereof, C is ##STR54## or mixtures thereof, wherein R is an alkyl group, an aryl group, an arylalkyl group, or mixtures thereof, and m and n are integers representing the number of repeating units; or (e) those of formulae I, III, IV, VII, and VIII wherein x is an integer of 0 or 1, A is ##STR55## B is ##STR56## wherein v is an integer of from 1 to about 20, EQU --(CH.sub.2 O).sub.t --
wherein t is an integer of from 1 to about 20, ##STR57## wherein z is an integer of from 2 to about 20, ##STR58## wherein u is an integer of from 1 to about 20, ##STR59## wherein w is an integer of from 1 to about 20, ##STR60## or mixtures thereof, C is ##STR61## or mixtures thereof, wherein R is an alkyl group, an aryl group, an arylalkyl group, or mixtures thereof, and m and n are integers representing the number of repeating units.
Copending application U.S. Ser. No. (not yet assigned; Attorney Docket No. D/96194Q2, filed concurrently herewith, with the named inventors Timothy J. Fuller, Leon A. Teuscher, Damodar M. Pai, John F. Yanus, Kathleen M. Carmichael, Edward F. Grabowski, and Paul F. Zukoski, the disclosure of which is totally incorporated herein by reference, discloses an imaging member which comprises a conductive substrate, a photogenerating material, a charge transport material, and a polymeric binder comprising (a) a first polymer comprising a polycarbonate, and (b) a second polymer of the formula ##STR62## wherein x is an integer of 0 or 1, A is ##STR63## or mixtures thereof, B is ##STR64## wherein v is an integer of from 1 to about 20, EQU --(CH.sub.2 O).sub.t --
wherein t is an integer of from 1 to about 20, ##STR65## wherein z is an integer of from 2 to about 20, ##STR66## wherein u is an integer of from 1 to about 20, ##STR67## wherein w is an integer of from 1 to about 20, ##STR68## or mixtures thereof, C is ##STR69## or mixtures thereof, wherein R is an alkyl group, an aryl group, an arylalkyl group, or mixtures thereof, and m and n are integers representing the numbers of repeating units.
Although excellent toner images may be obtained with multilayered belt photoreceptors that are developed with dry developer powder (toner), it has been found that these same photoreceptors may become unstable when employed with liquid development systems. The photoreceptors may suffer from cracking, crazing, crystallization of active compounds, phase separation of charge transporting molecules, and extraction of small molecule charge transport compounds caused by contact with the organic liquid vehicle, typically an isoparaffinic hydrocarbon such as one of the Isopar.RTM. materials commonly employed in liquid developers. The damaging results of contact with the hydrocarbon vehicle of the liquid developer can markedly degrade the mechanical integrity and electrical properties of the photoreceptor. More specifically, the organic carrier fluid of a liquid developer can leach out activating small molecules, such as arylamine containing compounds, typically used in charge transport layers. Examples of this class of arylamine materials are N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine, bis-(4-diethylamino-2-methylphenyl)-phenylmethane, 2,5-bis-(4'-dimethylaminophenyl)-1,3,4'-oxadiazole, 1-phenyl-3-(4'-dimethylaminostyryl-5-(4"-dimethylaminophenyl)pyrazoline, 1,1-bis-(4-(di-N,N'-p-methylphenyl)-aminophenyl)-cyclohexane, 4-diethylaminobenzaldehyde-1,1-diphenylhydrazone, and the like. The leaching process can result in crystallization of the small molecules, such as the aforementioned arylamine compounds, onto the photoreceptor surface and subsequent migration of the arylamine into the liquid developer. In addition, the developer vehicle, typically a C.sub.10 -C.sub.14 branched hydrocarbon, can induce the formation of cracks and crazes in the photoreceptor surface. These effects can lead to copy defects and shorter photoreceptor life. The degradation of the photoreceptor manifests as increased background and other printing defects prior to complete physical photoreceptor failure. The leaching out of the activating small molecule also increases the susceptibility of the transport layer to solvent/stress cracking when the belt is parked over a belt support roller during periods of non-use. Some liquid developer vehicles can also promote phase separation of the activating small molecules, such as arylamine compounds, in the transport layers, particularly when high concentrations of the arylamine compounds are present in the transport layer binder. Phase separation of active small molecules also adversely alters the electrical and mechanical properties of a photoreceptor. Similarly, single layer photoreceptors having a single active layer comprising photoconductive particles dispersed in a charge transport film-forming binder also are vulnerable to the same degradation problems encountered by the previously described multilayered type of photoreceptor when exposed to liquid developers. Although flexing is normally not encountered with rigid, cylindrical, multilayered photoreceptors which utilize charge transport layers containing activating small molecules dispersed or dissolved in a polymeric film forming binder, electrical degradation is similarly encountered during development with liquid developers. Sufficient degradation of these photoreceptors by liquid developers can occur in less than two hours as indicated by leaching of the small molecule and cracking of the matrix polymer film. Continuous exposure for a few days severely damages the photoreceptor. Thus, in advanced imaging systems utilizing multilayered photoreceptors exposed to liquid development systems, cracking and crazing have been encountered in critical charge transport layers during belt cycling. Cracks developing in charge transport layers during cycling can be manifested as print-out defects adversely affecting copy quality. Furthermore, cracks in the photoreceptor pick up toner particles which cannot be removed in the cleaning step and may be transferred to the background in subsequent prints. In addition, crack areas are subject to delamination when contacted with blade cleaning devices, thus limiting the options in electrophotographic product design.
For use with liquid developers, photoreceptors employing charge transport polymers have been developed, such as those described in U.S. Pat. No. 4,801,507, U.S. Pat. No. 4,806,644, U.S. Pat. No. 4,818,650, U.S. Pat. No. 4,806,443, and U.S. Pat. No. 5,030,532. While these compositions may meet machine requirements, the synthetic procedure to make these polymers are difficult and in some cases employ toxic substances. The acidic conditions employed in the syntheses also results in generation of free radicals, which in turn can result in material having properties that vary from batch to batch.
While known compositions and processes are suitable for their intended purposes, a need remains for improved electrostatic imaging members. In addition, a need remains for electrostatic imaging members which exhibit reduced or no crystallization when operated in an environment employing liquid ink development. Further, a need remains for electrostatic imaging members exhibiting improved imaging operation during extended image cycling. Additionally, a need remains for charge transport polymers which can be prepared by non-toxic syntheses. There is also a need for charge transport polymers with properties which remain constant from batch to batch. In addition, there is a need for charge transport polymers which exhibit improved wear resistance. Further, there is a need for high performance charge transport polymers which can be synthesized and scaled up in a non-toxic environment and which have reproducible properties from batch to batch.